In one aspect, the invention relates to an apparatus for feeding solids to a high pressure vessel. According to another aspect, the invention relates to a method for feeding such solids to a high pressure vessel.
There are many known processes wherein solids are transferred from a low pressure zone to a higher pressure zone. Examples of such processes include, for example, various pyrolysis, gasification, liquefaction, and extraction processes which utilize solid carbonaceous fuels. A common method of feeding solids from a low pressure zone to a high pressure zone involves gas-pressurized lock hoppers. According to such techniques, solids are introduced to the lock hopper at a low pressure and then a gas is pumped into the hopper so as to pressurize the hopper chamber to a high pressure. The solids are then discharged from the hopper so as to be transferred to the high pressure zone. The use of gases to pressurize the lock hopper has several distinct disadvantages. First, pressurization of the lock hopper with the gas requires a major portion of the cycle time. This has economic penalties since the hopper size to do a given job increases with the cycle time. Further, the gas used for pressurization will tend to mix with gases in the high pressure vessel to which solids are transferred. This causes dilution of the desired gas mix in the high pressure vessel and can interfere with critical process dynamics. This problem may become critical enough to require removal of the pressurizing gas from the gas stream in the high pressure vessel, thus increasing the cost of the system. Finally, valves utilized in a gas-pressurized lock hopper feed system must operate in a dusty abrasive environment, with a consequent short working life.
Some of the above discussed disadvantages of gas pressurized lock hoppers are overcome by a liquid sealed lock hopper system as described in U.S. Pat. No. 3,729,105 of Huebler et al. In this system, solids are transferred from a storage bin to a lock hopper which contains a liquid. Any overflow liquid is collected in a separate collecting vessel. Further liquid is supplied as needed to attain a pressure in the lock hopper which is substantially equal to the pressure of the high pressure vessel to which the solids are desired to be transferred. A valve is then opened at the outlet of the lock hopper so as to discharge the solids, the solids being allowed to drop into a feeder which conveys the solids to the high pressure vessel. Liquid contained in the feeder during transfer of the solids to the high pressure vessel provides a liquid seal between the high pressure vessel and the lock hopper. Thus, intermixing of gases from the lock hopper and high pressure vessel is inhibited. Smaller lock hoppers can be used in such a system since only a very short time is required to pressurize the lock hopper using a liquid due to the relative incompressibility of the liquid. Valve life is also lengthened due to the use of a liquid rather than a gas.
Although the above described liquid sealed system is a considerable improvement over gaseous systems, improvement would be desirable, particularly with respect to efficiency.